Resistive random access memory device

ABSTRACT

A memory architecture includes: a plurality of cell arrays each of which comprises a plurality of bit cells, wherein each of bit cells of the plurality of cell arrays uses a respective variable resistance dielectric layer to transition between first and second logic states; and a control logic circuit, coupled to the plurality of cell arrays, and configured to cause a first information bit to be written into respective bit cells of a pair of cell arrays as an original logic state of the first information bit and a logically complementary logic state of the first information bit, wherein the respective variable resistance dielectric layers are formed by using a same recipe of deposition equipment and have different diameters.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 17/003,761, filed on Aug. 26, 2020, which is a continuation ofU.S. patent application Ser. No. 16/158,498, filed on Oct. 12, 2018, nowU.S. Pat. No. 10,762,960, which claims priority to U.S. ProvisionalPatent Application No. 62/592,574, filed on Nov. 30, 2017, each of whichis incorporated by reference herein in its entirety.

BACKGROUND

Integrated circuits that serve as memory devices or include memoryportions are very popular and serve a variety of functions in theelectronics world. Resistive random-access memory (RRAM) devices arenon-volatile memory type devices formed using semiconductormanufacturing methods. The RRAM device bears some similarities toconductive-bridging RAM (CBRAM) and phase change memory devices.

Generally, RRAM devices operate under the principle that a dielectric,which is normally insulating, can be made to conduct through a filamentor conduction path formed after the application of a sufficiently highvoltage. The conduction path formation can arise from differentmechanisms, including but not limited to defect, metal migration, oxygenvacancy, etc. Various different dielectric materials may be used in RRAMdevices. Once the filament or conduction path is formed, it may bereset, i.e. broken, resulting in a high resistance state (HRS) or set,i.e. re-formed, resulting in a lower resistance (LRS), by anappropriately applied voltage, respectively.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that various features are not necessarily drawn to scale. In fact,the dimensions of the various features may be arbitrarily increased orreduced for clarity of discussion.

FIG. 1 illustrates an exemplary block diagram of a resistive randomaccess memory (RRAM) architecture, in accordance with some embodiments.

FIG. 2 illustrates an exemplary block diagram of an RRAM macro of theRRAM architecture of FIG. 1 in accordance with some embodiments.

FIG. 3 illustrates an exemplary schematic diagram of an RRAM cell of oneof the RRAM cell arrays of the RRAM macro 108 of FIG. 2 , in accordancewith some embodiments.

FIG. 4 illustrates an exemplary schematic diagram of the RRAMarchitecture of FIG. 1 , in accordance with some embodiments.

FIG. 5A illustrates an exemplary schematic diagram of a word line (WL)signal source circuit of the RRAM architecture of FIG. 1 , in accordancewith some embodiments.

FIG. 5B illustrates an exemplary schematic diagram of a bit line (BL)signal source circuit of the RRAM architecture of FIG. 1 , in accordancewith some embodiments.

FIG. 5C illustrates an exemplary schematic diagram of a sense amplifierand a portion of an input/output (I/O) circuit of the RRAM architectureof FIG. 1 , in accordance with some embodiments.

FIG. 5D illustrates exemplary operation comparisons between two types ofsensing amplifier circuits, in accordance with some embodiments.

FIG. 6 illustrates a flow chart of an exemplary method to operate theRRAM architecture of FIG. 1 , in accordance with some embodiments.

FIG. 7 illustrates a flow chart of an exemplary method to fabricate theRRAM macro of FIG. 2 , in accordance with some embodiments.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The following disclosure describes various exemplary embodiments forimplementing different features of the subject matter. Specific examplesof components and arrangements are described below to simplify thepresent disclosure. These are, of course, merely examples and are notintended to be limiting. For example, the formation of a first featureover or on a second feature in the description that follows may includeembodiments in which the first and second features are formed in directcontact, and may also include embodiments in which additional featuresmay be formed between the first and second features, such that the firstand second features may not be in direct contact. Additionally, it willbe understood that when an element is referred to as being “connectedto” or “coupled to” another element, it may be directly connected to orcoupled to the other element, or one or more intervening elements may bepresent.

In recent years, unconventional nonvolatile memory (NVM) devices, suchas ferroelectric random access memory (FRAM) devices, magnetic randomaccess memory (MRAM) devices, phase-change random access memory (PRAM)devices, and resistive random access memory (RRAM) devices, haveemerged. In particular, RRAM devices, which exhibit a switching behaviorbetween a high resistance state and a low resistance state, have variousadvantages over conventional NVM devices. Such advantages include, forexample, compatible fabrication steps with currentcomplementary-metal-oxide-semiconductor (CMOS) technologies, low-costfabrication, a compact structure, flexible scalability, fast switching,high integration density, etc.

In general, an RRAM device, or more particularly an RRAM cell, includesan upper (anode) electrode and a lower (cathode) electrode with avariable resistance dielectric layer interposed between the upper andlower electrodes. In some examples, an RRAM cell may further include acapping layer interposed between the upper electrode and the variableresistance dielectric layer thereby causing the RRAM cell to have abipolar switching behavior. The term “bipolar” as used herein refers tothe two voltage polarities of an RRAM cell that exhibits a firstconductive behavior with a first polarity of voltage applied across theupper and lower electrodes, and a second conductive behavior with asecond polarity (a polarity opposite to the first polarity) of voltageapplied across the upper and lower electrodes.

As described above, during a write operation to the RRAM cell, a ‘set’voltage is applied across the upper and lower electrodes to change thevariable resistance dielectric layer from a first resistivity (e.g., ahigh resistance state (HRS)) to a second resistivity (e.g., a lowresistance state (LRS)). Similarly, a ‘reset’ voltage is applied acrossthe upper and lower electrodes to change the variable resistancedielectric layer from the second resistivity back to the firstresistivity, for example, from LRS to HRS. Therefore, in instances wherethe LRS and HRS correspond to logic “1” and logic “0” states (or viceversa), respectively, the ‘set’ and ‘reset’ voltages can be used tostore digital information bits in the RRAM cell.

Various figures-of-merit are used to assess performance of an RRAM cell.In particular, among the various figures-of-merit, endurance of an RRAMcell is generally used to assess for which application the RRAM cell issuitable. Endurance of an RRAM cell is referred to the number of cycles(from HRS to LRS, or vice versa) the RRAM cell can endure before the HRSand LRS of the RRAM cell become indistinguishable. Depending on the typeof application in which an RRAM cell will be used, an RRAM cell with aparticular endurance level or range may be selected for a certainapplication. For example, when an RRAM cell is used for an electricalfuse (eFuse), the endurance of the eFuse RRAM cell is typically lessthan about 10 cycles. In another example, when an RRAM cell is used as amulti-time programmable (MTP) memory device, the endurance of the MTPRRAM device is typically between about 10 and 1,000 cycles. Yet inanother example, when an RRAM cell is used to store data (e.g., a flashmemory device), the endurance of such an RRAM cell is typically betweenabout 10,000 and 100,000 cycles. The figures-of-merit (e.g., endurance,retention time, etc.) of an RRAM cell may be determined by selecting aparticular thickness and/or crystalline structure of the variableresistance dielectric layer in the RRAM cell, as described in furtherdetail below.

In order to fabricate an RRAM device having plural RRAM cells on asingle chip/die that can be used in multiple applications that eachrequires a respective different endurance, conventionally, multiplerecipes to form multiple variable resistance dielectric layers, eachwith different thickness and/or crystalline structure, are typicallyused. As such, extra amounts of time/cost/fabrication steps may be usedto produce an RRAM device that can be used in two or more applications.Thus, the conventional RRAM devices have not been entirely satisfactoryin every aspect.

Embodiments of the present disclosure provide a novel RRAM architecturethat includes a plurality of RRAM cell arrays integrated as an RRAMmacro, wherein each RRAM cell array includes a plurality of RRAM cells.In some embodiments, at least a pair of the plurality of RRAM cellarrays are configured to present one information bit as twocomplementary logic states at respective RRAM cells through writeoperations. That is, an RRAM cell of one of the pair of RRAM cell arraysis configured to present an information bit as its original logic state;and an RRAM cell of the other of the pair of RRAM cell array pairs isconfigured to present the information bit as its complementary logicstate. As such, when compared to conventional RRAM devices that rely ona fixed reference current signal to read out respective logic states,the pair of RRAM cell arrays of the disclosed RRAM architecture canpresent a greater difference between respective read current signalswhile being read out, which in turn can lower magnitudes of writevoltage signals (e.g., the set/reset voltages as mentioned above). Thus,such a pair of RRAM cell arrays may be used in applications that requirehigher endurance.

Further, in some embodiments, the RRAM macro may include at least oneRRAM cell array, different from the pair of RRAM cell arrays, that isconfigured to present information bits in their respective logic states.Such an RRAM cell array may be used in applications that require lowerendurance, in accordance with some embodiments. In some embodiments,each RRAM cell array of the RRAM macro uses an universal variableresistance dielectric layer with a particular thickness and/orcrystalline structure, formed by using a single same recipe, in itsrespective PRAM cells. Thus, even when only a single recipe is used toform the respective variable resistance dielectric layers, the disclosedRRAM architecture can incorporate multiple PRAM cell arrays suitable formultiple applications (e.g., eFuse, MTP, data storage, etc.) on a singlechip by using the single recipe without the requirements of extraamounts of time/cost/fabrication steps, as seen in conventional RRAMdevices. This is because different RRAM cell arrays on the single chipcan have different memory elements, e.g. the variable resistancedielectric layers, in terms of different diameters to satisfy differentoperating endurances.

FIG. 1 illustrates an exemplary block diagram of a disclosed RRAMarchitecture 100 in accordance with various embodiments. As shown, theRRAM architecture 100 is formed on a single chip/die 102, and the RRAMarchitecture 100 includes a control logic circuit 104, a signal sourcecircuit 106 coupled to the control logic circuit 104, and at least oneRRAM macro 108 coupled to the control logic circuit 104 and the signalsource circuit 106, respectively. While any number of RRAM macros may beintegrated into the RRAM architecture 100 and remain within the scope ofthe present disclosure, for clarity of discussion, one RRAM macro (e.g.,108) is shown in the illustrated embodiment of FIG. 1 .

In some embodiments, the RRAM macro 108 includes a plurality of RRAMcell arrays, each of which includes a plurality of RRAM cells, whichwill be discussed with reference to FIGS. 2 and 3 . In some embodiments,the control logic circuit 104 is configured to cause at least a pair ofthe plurality of RRAM cell arrays to present a single information bit asits original and complementary logic states so as to suit such a pair ofRRAM cell arrays for higher-endurance applications; and cause at leastanother one of the plurality of RRAM cell arrays to present a singleinformation bit at its original logic state so as to suit such an RRAMcell array for lower-endurance applications. In some embodiments, thesignal source circuit 106, which may be provided by a voltage converter(e.g., a charge pump), is configured to provide one or more voltagesignals to the RRAM cells of the RRAM macro 108 for respectiveread/write operations. Details of the signal source circuit 106 will bediscussed with reference to FIGS. 5A and 5B.

FIG. 2 illustrates a top view of an exemplary block diagram of the RRAMmacro 108 of the RRAM architecture 100 of FIG. 1 , in accordance withsome embodiments. Other RRAM macros of the RRAM architecture 100 notshown in FIG. 1 may be each substantially similar to the illustratedembodiment of RRAM macro 108 of FIG. 2 . As shown in FIG. 2 , the RRAMmacro 108 includes RRAM cell arrays 202, 204, and 206, word line (WL)drivers 208, 210, and 212, a top sink 214, a bottom sink 216, and aninput/output (I/O) circuit 218. Although the RRAM macro 108 includesthree RRAM cell arrays in the illustrated embodiment of FIG. 2 , it isunderstood that the RRAM macro 108 may include any plurality number ofRRAM cell arrays while remaining within the scope of the presentdisclosure.

In some embodiments, each RRAM cell array of the RRAM macro 108 iscoupled with a respective WL driver. For example, the RRAM cell array202 is coupled with the WL driver 208; the RRAM cell array 204 iscoupled with the WL driver 210; and the RRAM cell array 206 is coupledwith the WL driver 212. On the other hand, the top and bottom sinks214/216, and the I/O circuit 218 (which includes sensing amplifier(s),multiplexers(s), bit line (BL) driver(s), etc., as will be discussedbelow) may be shared by the RRAM cell arrays 202-206, in accordance withsome embodiments of the present disclosure. Alternatively stated, thetop and bottom sinks 214/216 and I/O circuit 218 may be globally used bythe top and bottom sinks 214/216 and I/O circuit 218 while operating theRRAM macro 108.

In some embodiments, the RRAM cell array 202 has a different memoryelement size or diameter from those of the RRAM cell arrays 204, 206.For example, each cell in the RRAM cell array 202 may have a smallerdiameter, which means a higher operating voltage level and a lowerendurance, compared to a cell in the RRAM cell arrays 204, 206. This maybe applied when all RRAM cell arrays 202, 204, 206 are same type ofcircuits (e.g. all 1c1b circuits by utilizing one cell to represent onebit). For different cells to achieve different diameters but samethickness and crystalline structure, a same recipe may be used tofabricate the cells by controlling the layout sizes of the cells. Forexample, an RRAM cell array 202 having an endurance of e.g. 1 to 10cycles and RRAM cell arrays 204, 206 having an endurance of e.g. 10,000and 100,000 cycles can be manufactured in one RRAM macro using a samerecipe.

FIG. 3 illustrates an exemplary schematic diagram of an RRAM cell 300 ofone of the RRAM cell arrays 202/204/206 of the RRAM macro 108 of FIG. 2, in accordance with some embodiments. In the illustrated embodiment ofFIG. 3 , the exemplary RRAM cell 300 includes a resistor 302 and atransistor 304 coupled to the resistor 302 in series, which can utilizedto provide respective resistor and transistor of each of other RRAMcells of the RRAM cell arrays 202/204/206, respectively. Such an RRAMcell 300 is typically referred to as a 1-transistor-1-resistor (1T1R)configuration. Although, in FIG. 3 , the RRAM cells (e.g., 300) of theRRAM cell arrays 202/204/206 are implemented as the 1T1R configuration,any of a variety of structures that exhibits a characteristic ofvariable resistance may be used by the RRAM cells of the RRAM cellarrays 202/204/206 such as, for example, a 1-diode-1-resistor (1D1R)configuration, a 1-selector-1-resistor (1S1R) configuration, a1-transistor-many resistors (1T-manyR) configuration, etc., whileremaining within the scope of the present disclosure.

As shown in FIG. 3 , the resistor 302 is formed as a multi-layer stackthat includes a top electrode 312, a capping layer 322, a variableresistance dielectric layer 332, and a bottom electrode 342. In someembodiments, the top electrode 312 may be formed from at least one ofthe materials selected from: Pt, TiN/Ti, TiN, Ru, Ni, and combinationsthereof; the capping layer 322 may be formed from at least one of thetransition metal materials such as, Ti, Ni, Hf, Nb, Co, Fe, Cu, V, Ta,W, Cr, and combinations thereof; the variable resistance dielectriclayer 332 may be formed from at least one of the transition metal oxidematerials such as, TiO_(x), NiO_(x), HfO_(x), NbO_(x), CoO_(x), FeO_(x),CuO_(x), VO_(x), TaO_(x), WO_(x), CrO_(x), and combinations thereof; andthe bottom electrode 342 may be formed of at least one of the materialsselected from: TiN, TaN, W, Pt, and combinations thereof. In someembodiments, the variable resistance dielectric layer 332 may include ahigh-k dielectric layer.

To operate (e.g., write a logic state to) the RRAM cell 300 formed asthe 1T1R configuration, generally, the transistor 304 is first activated(i.e., turned on) by an enabling/selecting signal through a word line(WL) connected to a gate of the transistor 304, and then a voltagesignal (e.g., a set voltage, or a reset voltage) is applied across theRRAM cell 300 through a bit line (BL) and a source line (SL) connectedto the top electrode 312 of the resistor 302 and a source of thetransistor 304, respectively. For example, to write a logic 1 to theRRAM cell 300, a set voltage is applied across the RRAM cell 300 (e.g.,the BL is applied with the set voltage while the SL is connected toground, or the SL is applied with the set voltage while the BL isconnected to ground) to cause the variable resistance dielectric layer332 to switch to the LRS (low resistance state); and to write a logic 0to the RRAM cell 300, a reset voltage, with a lower magnitude than theset voltage, is applied across the RRAM cell 300 (e.g., the BL isapplied with the reset voltage while the SL is connected to ground, orthe SL is applied with the reset voltage while the BL is connected toground) to cause the variable resistance dielectric layer 332 to switchto the HRS (high resistance state). Similarly, to read out the writtenlogic state from the RRAM cell 300, after the transistor 304 isactivated, a read voltage, typically with a lower magnitude than themagnitudes of the set and reset voltages, is applied across the RRAMcell 300, and based on a magnitude of a current signal (which variesbecause of the resistance state of the variable resistance dielectriclayer 332) conducting through the RRAM cell, the logic state writteninto the RRAM cell 300 can be determined.

In some embodiments, respective polarities of the set and reset voltagesto write an RRAM cell are not necessarily to be the same. Specifically,when the polarities are the same (e.g., both positive, or bothnegative), the RRAM cell is typically referred to as a unipolar RRAMcell; and when the polarities are different from each other (e.g., oneis positive and the other is negative), the RRAM cell is typicallyreferred to as a bipolar RRAM cell. In accordance with some embodiments,each RRAM cell of the RRAM cell arrays 202/204/206 of the RRAM macro 108can be either a bipolar or a unipolar RRAM cell.

In general, the variable resistance dielectric layer (e.g., a transitionmetal oxide layer) 332 is formed by deposition, for example, atomiclayer deposition (ALD), chemical vapor deposition (CVD), meta-organicchemical vapor deposition (MOCVD), etc., to have a particular thicknessand crystalline structure using a particular recipe. A recipe mayinclude a variety of control parameters to control the depositionequipment, for example, gas flow rate, chamber pressure, partialpressure of a gas line, temperature, etc. To form a variable resistancedielectric layer with a particular thickness and crystalline structure,a particular value for each of the variety of control parameters may beselected. In some embodiments, the RRAM cells of the RRAM cell arrays202/204/206 of the RRAM macro 108 are each formed by a single recipe.

FIG. 4 illustrates an exemplary circuit schematic diagram 400 of theRRAM architecture 100 of FIG. 1 , in accordance with some embodiments.Although in the exemplary circuit schematic diagram 400 of FIG. 4 , theRRAM cell arrays 202, 204, and 206 each includes one RRAM cell, it isunderstood that, in some embodiments, the RRAM cell arrays 202, 204, and206 each includes a plurality of RRAM cells arranged in a column-rowconfiguration, wherein each row includes a respective WL and each columnincludes respective BL and SL and each of the plurality of RRAM cells isarranged at a respective intersection of column (BL/SL) and row (WL).

For example, the RRAM cell 402 of the plurality of RRAM cells of theRRAM cell array 202 is arranged at an intersection of a first row ofplural rows (e.g., a row including WL 410) and a first column of pluralcolumns (e.g., a column including BL 408-1 and SL 412-1) of the RRAMcell array 202; the RRAM cell 404 of the plurality of RRAM cells of theRRAM cell array 204 is arranged at an intersection of a first row ofplural rows (e.g., a row including WL 414) and a first column of pluralcolumns (e.g., a column including BL 408-2 and SL 412-2) of the RRAMcell array 204; and the RRAM cell 406 of the plurality of RRAM cells ofthe RRAM cell array 206 is arranged at an intersection of a first row ofplural rows (e.g., a row including WL 416) and a first column of pluralcolumns (e.g., a column including BL 408-3 and SL 412-3) of the RRAMcell array 206.

Further, in some embodiments, the RRAM cells of the RRAM cell arrays202, 204 and 206 may be each implemented as an 1T1R RRAM cell formed bya resistor and a transistor that are coupled in series (FIG. 3 ). Suchan 1T1R RRAM cell is formed as a three terminal device, wherein thethree terminals are respectively coupled to corresponding BL, WL, andSL.

As illustrated in the example of FIG. 4 , the RRAM cell array 202includes an RRAM cell 402 formed by a resistor 402R and a transistor402T that are coupled in series; the RRAM cell array 204 includes anRRAM cell 404 formed by a resistor 404R and a transistor 404T that arecoupled in series; and the RRAM cell array 206 includes an RRAM cell 406formed by a resistor 406R and a transistor 406T that are coupled inseries. Further, the RRAM cell 402 is coupled to the BL 408-1 (throughan end of the resistor 402R not connected to the transistor 402T), WL410 (through a gate of the transistor 402T), and SL 412-1 (through asource of the transistor 402T); the RRAM cell 404 is coupled to the BL408-2 (through an end of the resistor 404R not connected to thetransistor 404T), WL 414 (through a gate of the transistor 404T), and SL412-2 (through a source of the transistor 404T); and the RRAM cell 406is coupled to the BL 408-3 (through an end of the resistor 406R notconnected to the transistor 406T), WL 416 (through a gate of thetransistor 406T), and SL 412-3 (through a source of the transistor406T).

It is understood that in some embodiments, the BL 408-1 of the RRAM cellarray 202 may be coupled to the BL 408-2 of the RRAM cell array 204, butisolated from the BL 408-3 of the RRAM cell array 206 for the purposesof avoiding cross-talk of signals when two RRAM cells on the sides ofthe I/O circuit 218 (e.g., RRAM cells 404 and 046) are concurrentlyaccessed. Similarly, the SL 412-1 of the RRAM cell array 202 may becoupled to the SL 412-2 of the RRAM cell array 204, but isolated fromthe SL 412-3 of the RRAM cell array 206 for the same purposes.

In some embodiments, the RRAM cell arrays 202, 204, and 206 are eachcoupled to the signal source circuit 106 through the respective WLdrivers 208/210/212, as mentioned above. More specifically, the RRAMcell arrays 202, 204, and 206 are coupled to a WL signal source circuit106W of the signal source circuit 106 through respective WL drivers 208,210, and 212 via corresponding WL's 410, 414, and 416. In someembodiments, each of the WL drivers 208/210/212 includes a pull-uptransistor (e.g., a p-type MOSFET) and a pull-down transistor (e.g., ann-type MOSFET) that are coupled to each other in series. It isunderstood that the pull-up and pull-down transistors may be eachimplemented as any of various other types of transistors while remainingwithin the scope of the present disclosure.

For example, the WL driver 208 includes a pull-up transistor 418U and apull-down transistor 418D; the WL driver 210 includes a pull-uptransistor 420U and a pull-down transistor 420D; and the WL driver 212includes a pull-up transistor 422U and a pull-down transistor 422D. Bothof the pull-up and pull-down transistors in each of the WL drivers 208,210, and 212 are coupled to the control logic circuit 104 at theirrespective gates and controlled by the control logic circuit 104 to beselectively turned on/off, and the pull-up transistors in each of the WLdrivers 208, 210, and 212 are coupled to the WL signal source circuit106W at their respective sources to receive a WL voltage signal 423, aswill be discussed below. Details of the WL signal source circuit 106Wwill be discussed with reference to FIG. 5A.

In some embodiments, the top and bottom sinks 214 and 216 mayrespectively include one or more transistors (426, 428, and 430) and(432, 434, and 436) that are each controlled by the control logiccircuit 104 to be selectively turned on/off. The transistors 426, 428,430, 432, 434, and 436 may be each implemented as an n-type MOSFET, orany of various other types of transistors while remaining within thescope of the present disclosure. In some embodiments, the I/O circuit218 may include transistors 438, 440, 442, 444, 446, and 448, aplurality of transmission gates 450, 452, 454, and 456, and a sensingamplifier (SA) 458.

In some embodiments, the I/O circuit 218 is selectively coupled to theRRAM cell of one or more of the RRAM cell arrays 202, 204, and 206 viacorresponding BL's and SL's. In particular, to be accessed (e.g., eitherwritten or read), the RRAM cell 402 of the RRAM cell array 202 isselected, by the control logic circuit 104, to be coupled by the I/Ocircuit 218 through activating the transmission gates 450 and 452; theRRAM cell 404 of the RRAM cell array 204 is selected, by the controllogic circuit 104, to be coupled by the I/O circuit 218 throughactivating the transmission gates 450 and 452; and the RRAM cell 406 ofthe RRAM cell array 206 is selected, by the control logic circuit 104,to be coupled by the I/O circuit 218 through activating the transmissiongates 454 and 456.

In some embodiments, while being written (i.e., correspondingtransmission gates have been activated), each RRAM cell of the RRAM cellarrays 202, 204, and 206 is configured to receive a BL voltage signal(e.g., a set voltage, or a reset voltage) 453 from a BL signal sourcecircuit 106B of the signal source circuit through the I/O circuit 218and then through a corresponding BL or SL. More specifically, thetransistors 442, 444, 446, and 448 may be controlled, by the controllogic circuit 104, to be selectively turned on/off so as to allow the BLvoltage signal 453 to be delivered to a desired RRAM cell through adesired BL or SL. The transistors 442, 444, 446, and 448 may be eachimplemented as an n-type MOSFET, or any of various other types oftransistors while remaining within the scope of the present disclosure.

In some embodiments, while being read (i.e., corresponding transmissiongates have been activated), the SA 458 is coupled to the RRAM cell ofone of the RRAM cell arrays 202, 204, and 206 through the transistors438 and 440 that are selectively turned on/off by the control logiccircuit 104, or the respective RRAM cells of two RRAM cell arraysdisposed on opposite sides of the I/O circuit 218 also through theselective on/off transistors 438 and 440. The transistors 438 and 440that function as passing gates may be each implemented as an n-typeMOSFET, or any of various other types of transistors while remainingwithin the scope of the present disclosure. Details of the BL signalsource circuit 106B and the SA 458 will be discussed with reference toFIG. 5B and FIG. 5C, respectively.

FIG. 5A illustrates an exemplary block diagram of the WL signal sourcecircuit 106W of FIG. 4 , in accordance with various embodiments. In theillustrated embodiment of FIG. 5A, the WL signal source circuit 106Wincludes a voltage converter 502 (e.g., a charge pump), a transistor 504(e.g., a p-type MOSFET), a comparator 506 (e.g., an amplifier), a firsttransmission gate 508, and a second transmission gate 510. In someembodiments, the comparator 506 has two input terminals and an outputterminal wherein one of the input terminals (e.g., an inverting inputterminal) is configured to receive a first reference voltage 511. Theoutput terminal of the comparator 506 is coupled to a gate of thetransistor 504, and the transistor 504 includes a source coupled to asecond reference voltage 513 (e.g., an input/output Vdd) and a draincoupled to the other of the input terminals (e.g., a non-inverting inputterminal) of the comparator 506 and the first transmission gate 508. Insome embodiments, the comparator 506 and the transistor 504 form alow-dropout (LDO) regulator that is configured to provide a voltagesignal 515 whose signal level is substantially close to the secondreference voltage 513.

Referring still to FIG. 5A, in some embodiments, the first transmissiongate 508 is configured to provide the WL voltage signal 423 based on thevoltage signal 515, which is substantially close to the second referencevoltage 513. In some other embodiments, the charge pump 502 isconfigured to provide the WL voltage signal 423 through the secondtransmission gate 510 when a desired signal level of the WL voltagesignal 423 is higher than the second reference voltage 513. In someembodiments, when the desired signal level of the WL voltage signal 423is not greater than the second reference voltage 513, the WL voltagesignal 423 is provided by the LDO regulator, formed by the comparator506 and the transistor 504, through the first transmission gate 508 suchthat the WL voltage signal 423's signal level may be equal to the secondreference voltage 513.

FIG. 5B illustrates an exemplary block diagram of the BL signal sourcecircuit 106B of FIG. 4 , in accordance with various embodiments. In theillustrated embodiment of FIG. 5B, the BL signal source circuit 106Bincludes a voltage converter 522 (e.g., a charge pump), a transistor 524(e.g., a p-type MOSFET), a comparator 526 (e.g., an amplifier), a firsttransmission gate 528, and a second transmission gate 530. In someembodiments, the comparator 526 has two input terminals and an outputterminal wherein one of the input terminals (e.g., an inverting inputterminal) is configured to receive a first reference voltage 523. Theoutput terminal of the comparator 526 is coupled to a gate of thetransistor 524, and the transistor 524 includes a source coupled to asecond reference voltage 527 (e.g., an input/output Vdd) and a draincoupled to the other of the input terminals (e.g., a non-inverting inputterminal) of the comparator 526 and the first transmission gate 528.Similar as the transistor 504 and comparator 506 of the WL signal sourcecircuit 106W as shown in FIG. 5A, the comparator 526 and the transistor524 form another low-dropout (LDO) regulator that is configured toprovide a voltage signal 525 whose signal level is substantially closeto the second reference voltage 527.

Referring still to FIG. 5B, in some embodiments, the first transmissiongate 528 is configured to provide the BL voltage signal 453 based on thevoltage signal 525, which is substantially close to the second referencevoltage 527. In some other embodiments, the charge pump 522 isconfigured to provide the BL voltage signal 453 through the secondtransmission gate 530 when a desired signal level of the BL voltagesignal 453 is higher than the second reference voltage 527. In someembodiments, when the desired signal level of the BL voltage signal 453is not greater than the second reference voltage 527, the BL voltagesignal 453 is provided by the LDO regulator, formed by the comparator526 and the transistor 524, through the first transmission gate 528 suchthat the BL voltage signal 453's signal level may be equal to the secondreference voltage 527. In some embodiments, the signal level of the WLvoltage signal 423 may correspond to the signal level of the BL voltagesignal 453. For example, the respective signal levels of the WL voltagesignals 423 may be different when the BL voltage signal 453 are equal tothe set and reset voltages, respectively.

FIG. 5C illustrates an exemplary circuit diagram of the SA 458 of FIG. 4, in accordance with various embodiments. As shown in the illustratedembodiment of FIG. 5C, the SA 458 is also coupled to two RRAM cells 540and 542 via a portion of the I/O circuit 218 (FIG. 4 ), herein referredto as “read circuit 544R,” and a bias generator circuit 548B. In someembodiments, the RRAM cells 540 and 542 represent the respective“being-read” RRAM cells of two different ones of the RRAM cell arrays202, 204, and 206 that are disposed on opposite sides of the I/O circuit218 such as, for example, RRAM cells 402 and 406, RRAM cells 404 and406, etc. Accordingly, each of the RRAM cells 540 and 542 is formed by aresistor and a serially coupled transistor, according to someembodiments. For example, the RRAM cell 540 is formed by resistor 540Rand transistor 540T; and the RRAM cell 542 is formed by resistor 542Rand transistor 542T.

In some embodiments, the SA 458 includes a first inverter 544, a secondinverter 546, a first transmission gate 548, a second transmission gate550, transistors 552, 554, 556, and 558. The first and second inverters544 and 546 are cross-coupled to form a latch (i.e., the first inverter544's input terminal coupled to the second inverter 546's outputterminal, and the second inverter 546's input terminal coupled to thefirst inverter 544's output terminal); the first transmission gate 548is coupled between the first inverter 544's input terminal/secondinverter 546's output terminal and node X; the second transmission gate550 is coupled between the first inverter 544's output terminal/secondinverter 546's input terminal and node Y; the transistor 552 (e.g., ap-type MOSFET) is coupled between a reference voltage 555 (e.g., Vdd)and the node X; and the transistor 554 (e.g., a p-type MOSFET) iscoupled between the reference voltage 555 and the node Y. In someembodiments, the first and second inverters 544 and 546, the first andsecond transmission gates s 548 and 550, and the transistors 552 and 554are configured to perform a sensing/amplifying function so as todetermine (e.g., read) logic states of the RRAM cells 540 and 542, whichwill be discussed below. The transistors 556 and 558 are respectivelycoupled to the nodes X and Y, and both coupled to the read circuit 544Rand the bias generator circuit 548B so as to control a read voltage forthe RRAM cells 540 and 542, which will be discussed below.

In some embodiments, the read circuit 544R includes transistors 560,562, 564, and 566, transmission gates 568 and 570, and a referencecurrent source 572. The transistors 560, 562, 564, and 566 may be eachimplemented as an n-type MOSFET, or any of various other types oftransistors while remaining within the scope of the present disclosure.The RRAM cell 540 is coupled to the SA 458 through the transistor 560and the transmission gate 568; and the RRAM cell 542 is coupled to theSA 458 through the transistor 562 and the transmission gate 570. In someembodiments, when the RRAM cells 540 and 542 represent the RRAM cells402 (or 404) and 406 (FIG. 4 ), respectively, the transistors 560 and562 may represent the transistors 438 and 440 (FIG. 4 ), respectively,and the transmission gates 568 and 570 may represent the transmissiongates 450 and 454 (FIG. 4 ), respectively. The read circuit 544R will bediscussed in further detail below when operations of the RRAMarchitecture 100 are discussed.

In some embodiments, the bias generator circuit 548B includes acomparator 573, transistors 574, 576, and 578, and a variable resistor580. The transistor 574 is implemented as a p-type MOSFET, and thetransistors 576 and 578 are each implemented as an n-type MOSFET. It isunderstood that the transistors 574 to 578 can be implemented as any ofvarious other types of transistors while remaining within the scope ofthe present disclosure. The comparator 573 has two input terminals andan output terminal wherein one of the input terminals (e.g., anon-inverting input terminal) is configured to receive a read voltage581. The output terminal of the comparator 573 is coupled to a gate ofthe transistors 576, and respective gates of the transistors 556 and 558of the SA 458. The transistor 576 includes a source coupled to the otherof the input terminals (e.g., an inverting input terminal) of thecomparator 573 and a drain of the transistor 578, and a drain coupled tothe reference voltage 555 through the transistor 574. The transistor 578is coupled to ground through the variable resistor 580, which can be apoly resistor in some embodiments. Further, in some embodiments, thebias generator circuit 548B is configured to provide a voltage signal583 based on the read voltage 581. The voltage signal 583 is coupled togates of the transistors 556 and 558. Such a voltage signal 583,controlled at the read voltage 581, can be used by the RRAM cells 540and/or 542 for respective read operations.

Since FIGS. 4-5C respectively illustrate at least a portion of the RRAMarchitecture 100, to illustrate the operation of the RRAM architecture100, reference numerals shown in FIGS. 4-5C are again used in thefollowing discussions. In some embodiments, the RRAM architecture 100can be used for multiple applications with respective differentendurances when different RRAM cell arrays in the RRAM macro 108 havedifferent RRAM element sizes and/or different operating voltage levels.For high-endurance applications, an information bit may be written to atleast two RRAM cells of the RRAM arrays, disposed at opposite sides ofthe I/O circuit 218, at its original and complementary logic states,respectively; and for low-endurance applications, an information bit maybe written to the RRAM cell of one of the RRAM arrays, disposed ateither side of the I/O circuit 218, at its original logic state.Operations of the RRAM architecture 100 to be used for thehigh-endurance and low-endurance applications will be respectivelydiscussed below.

In some embodiments, to operate the RRAM architecture 100 for thehigh-endurance applications, the control logic circuit 104 may firstselect a pair of RRAM cell arrays (e.g., 204 and 206). In someembodiments, the pair of RRAM cell arrays 204 and 206 are disposed onthe opposite sides of the I/O circuit 218. Upon determining the RRAMcell arrays 204 and 206 to be used for high-endurance applications, thecontrol logic circuit 104 selects one RRAM cell from the RRAM cell array204 to be written into an original logic state of an information bit(e.g., RRAM cell 404), and one RRAM cell from the RRAM cell array 206 tobe written into a complementary logic state of the information bit(e.g., RRAM cell 406). In other words, one of the RRAM cells 404 and 406is set (therefor presenting a logic 1), and the other of the RRAM cells404 and 406 is reset (therefore presenting a logic 0).

To access the RRAM cell 404, the control logic circuit 104 asserts theRRAM cell 404's respective WL 414 by complementarily turning on/off thetransistors 420U and 420D of the WL driver 210 (e.g., turning on thetransistor 420U and off the transistor 420D), and BL 408-2 and SL 412-2by activating the transmission gates 450 and 452 of the I/O circuit 218.Accordingly, the control logic circuit 104 can allow the WL signalsource circuit 106W to provide the WL voltage signal 423 to the selectedRRAM cell 404 through the asserted WL 414 to activate (turn on) thetransistor 404T of the RRAM cell 404. Simultaneously or subsequently,the control logic circuit 104 can allow the BL signal source circuit106B to provide the BL voltage signal 453 at a signal level of the setvoltage to the RRAM cell 404 through the BL 408-2 or SL 412-2 so as towrite a logic 1 to the RRAM cell 404. More specifically, during such awrite operation, the control logic circuit 104 may turn off thetransistors 438 to isolate the SA 458 from accessing the RRAM cell 404,and turn on the transistor 442 (while turning off the transistor 444) toallow the BL voltage signal 453 to be delivered to the RRAM cell 404 viathe SL 412-2 or turn on the transistor 444 (while turning off thetransistor 442) to allow the BL voltage signal 453 to be delivered tothe RRAM cell 404 via the BL 408-2.

In some embodiments, to access the RRAM cell 406, the control logiccircuit 104 asserts the RRAM cell 406's respective WL 416 bycomplementarily turning on/off the transistors 422U and 422D of the WLdriver 212 (e.g., turning on the transistor 422U and off the transistor422D), and BL 408-3 and SL 412-3 by activating the transmission gates454 and 456 of the I/O circuit 218. Accordingly, the control logiccircuit 104 can allow the WL signal source circuit 106W to provide theWL voltage signal 423 to the selected RRAM cell 406 through the assertedWL 416 to activate (turn on) the transistor 406T of the RRAM cell 406.Simultaneously or subsequently, the control logic circuit 104 can allowthe BL signal source circuit 106B to provide the BL voltage signal 453at a signal level of the reset voltage to the RRAM cell 406 through theBL 408-3 or SL 412-3 so as to write a logic 0 to the RRAM cell 406. Morespecifically, during such a write operation, the control logic circuit104 may turn off the transistors 438 to isolate the SA 458 fromaccessing the RRAM cell 406, and turn on the transistor 446 (whileturning off the transistor 448) to allow the BL voltage signal 453 to bedelivered to the RRAM cell 406 via the SL 412-3 or turn on thetransistor 448 (while turning off the transistor 446) to allow the BLvoltage signal 453 to be delivered to the RRAM cell 406 via the BL408-3. It is noted that the write operations performed on the RRAM cells404 and 406 do not necessarily occur at the same time, in accordancewith some embodiments of the present disclosure.

After the RRAM cells 404 and 406 are respectively written into theoriginal logic state (logic 1) and complementary logic state (logic 0)of the information bit, the control logic circuit 104 may concurrentlyread the respective logic states from the RRAM cells 404 and 406, inaccordance with various embodiments. Similar as the write operationdescribed above, the RRAM cells 404 and 406 are allowed to be read byasserting respective WL's 414 and 416 (through complementarily turningon/off the transistors 420U/420D and 422U/422D), and BL's 408-2 and408-3 and SL's 412-2 and 412-3 (through activating the transmissiongates 450, 452, 454, and 456). To read out the logic states present bythe RRAM cells 404 and 406, in some embodiments, the control logiccircuit 104 may turn off the transistors 442, 444, 446, and 448 toisolate the BL voltage signal 453 from the RRAM cells 404 and 406, andturn on the transistors 438 and 440 to allow the SA 458 to access theRRAM cells 404 and 406.

Referring again to FIG. 5C, as mentioned above, the two RRAM cells 540and 542 represent the RRAM cells being read (i.e., the RRAM cell 404 and406 in the current example), the transistors 560 and 562 respectivelyrepresent the being-read RRAM cells' corresponding pass gate transistors438 and 440 (FIG. 4 ), and the transmission gates 568 and 570respectively represent the being-read RRAM cells' correspondingtransmission gates 450 and 454 (FIG. 4 ). In some embodiments, to readthe respective logic states from the two RRAM cells 540 (e.g., 404) and542 (e.g., 406) that are disposed in different arrays, the control logiccircuit 104 may first turn off the transistors 564 and 566 to isolatethe reference current source 572 from the RRAM cells from the RRAM cells540 and 542. However, in some embodiments, the control logic circuit 104may complementarily turn on the transistors 564 and 566 when only one ofthe RRAM cells 540 and 542 is read, which will be discussed below.

Referring still to FIG. 5C, in some embodiments, the control logiccircuit 104 may turn on the transistor 574 to activate the biasgenerator circuit 548B. Upon being activated, an LDO circuit, formed bythe comparator 573 and the transistor 576, is configured to provide thevoltage signal 583 with a signal level substantially close to the readvoltage 581. Further, such an LDO circuit may rely on the transistor 578and the variable resistor 580 that can simulate a loading of the readRRAM cells 540/542 so as to provide a more reliable read voltage to theRRAM cells 540 and 542. As mentioned above, the transistors 556 and 558are configured to receive the voltage signal 583 at the read voltage asprovided by the bias generator circuit 548B. In some embodiments, such aread voltage is applied to the RRAM cell 540 (e.g., 404) via the SL412-2 and the RRAM cell 542 (e.g., 406) via the SL 412-3 while therespective BL's 408-2 and 408-3 may be coupled to ground. Since therespective transistors 404T and 406T of the RRAM cells 540 (e.g., 404)and 542 (e.g., 406) are turned on (i.e., both representing asubstantially similar ON resistance), current signals 591 and 593 (FIG.5C) conducting through the respective resistors 404R of the RRAM cell540, which has been set to the LRS, and 406R of the RRAM cell 542, whichhas been reset to the HRS, may have respective different signal levels.In some embodiments, the current signals 591 and 593 may be concurrentlygenerated to respectively conduct through the RRAM cells 540 and 542.More specifically, in the current example where the RRAM cells 540 and542 respectively represent the RRAM cells 404 and 406 (FIG. 4 ), thecurrent signal 591 may flow through the SL 412-2, the transistor 404T,the resistor 404R, the BL 408-2, optionally the BL 408-1, thetransistors 428 and 426, and to ground; the current signal 593 may flowthrough the SL 412-3, the transistor 406T, the resistor 406R, the BL408-3, the transistors 432 and 434, and to ground. In some embodiments,the transistors 426, 428, 430, 432, 434, and 436 may be selectivelyturned on or off by the control logic circuit 104. In some embodiments,the current signals 591 and 593 are referred to as the information bit'scorresponding LRS and HRS current signals, respectively.

In some embodiments, such two current signals 591 and 593 may changevoltage levels at the nodes X and Y until respective voltage levels(i.e., logic states) at the nodes X and Y are latched (i.e., fixed) bythe cross-coupled inverters 544 and 546. In some embodiments, prior tothe current signals 591 and 593 changing the voltage levels at the nodesX and Y, the control logic circuit 104 may turn on the transistors 552and 554 to pre-charge the inverters 544 and 546 through the transmissiongates 548 and 550, which are optional. After the voltage levels (i.e.,logic states) at the nodes X and Y are latched (or determined) by the SA458, the control logic circuit 104 may accordingly determine therespective logic states present by the RRAM cells 540 (e.g., 404) and542 (e.g., 406). In the current example, the logic states of the RRAMcells 404 and 406 determined by the control logic circuit 404 may be alogic 1 and a logic 0, respectively.

The control logic circuit 104 of the disclosed RRAM architecture 100determines a logic state of an information bit by comparing twodifferent current signals conducting through two RRAM cells that werewritten to an information bit's original and complementary logic states,respectively. By doing so, the SA 458 can more efficiently determine theoriginal logic state of the information bit. This is because in theexisting RRAM device whose RRAM's logic state can only be determined bycomparing a current signal conducting therethrough with a pre-definedreference current. And a current level of the pre-defined referencecurrent is typically chosen to be in the middle of current levels of twostatistic current signals (one is a statistically determined HRS currentsignal of the existing RRAM device, and the other is a statisticallydetermined LRS current signal of the existing RRAM device) so as toallow a corresponding SA to correctly determine whether the logic statepresent by the RRAM cell is a logic 1 or 0. As such, a current leveldifference between the reference current and a to-be determined currentsignal (either a LRS current signal or a HRS current signal) conductingthrough any RRAM cell is relatively small. In stark contrast, the SA 458of the disclosed RRAM architecture 100 relies on two different currentsignals that have been intentionally conducted as one information bit'scorresponding HRS and LRS current signals, which can have asubstantially greater current level difference therebetween, todetermine the original logic state of the information bit. As a result,when writing a pair of RRAM cells to cause them to respective conduct aninformation bit's corresponding HRS and LRS current signals, in turn,the voltage levels of the respective set and reset voltages (i.e. thewrite voltages) can be substantially lower, which allows the RRAM cellsto have a higher endurance.

In some embodiments, operating the RRAM architecture 100 to be used forthe low-endurance applications is substantially similar to thehigh-endurance applications as discussed above except that the controllogic circuit 104 may cause an information bit to be written into theRRAM cell(s) of one RRAM cell array (e.g., the RRAM cell 402 of the RRAMcell array 202) of the RRAM architecture 100 as its original logicstate. Since writing the information bit into the RRAM cell 402 as itsoriginal logic state is substantially similar to writing the RRAM cell404, as discussed above, the discussion is not repeated here. In someembodiments, when reading the logic state written into the RRAM cell402, a reference current source may be used. Referring again to FIGS. 4and 5C concurrently, when reading the RRAM cell 402 (corresponding tothe being-read RRAM cell 540 in FIG. 5C), the control logic circuit 104may turn on the transistor 438 (corresponding to the transistor 560 inFIG. 5C) and turn off the transistor 440 (corresponding to thetransistor 562 in FIG. 5C), and turn on the transistor 566 and turn offthe transistor 564. As such, the SA 458 can compare the current signal591 conducting through the RRAM cell 540 (e.g., 402) with the areference current provided by the reference current source 572 so as todetermine (read) the logic state of the information bit written to theRRAM cell 540 (e.g., 402). As a result, when writing an RRAM cell toconduct an information bit's corresponding HRS or LRS current signal(depending on the information bit's original logic state), in turn, theRRAM cell may have a lower endurance.

Based on the above-discussed operations of the RRAM architecture 100, itis understood that the control logic circuit 104 can be used in multipleapplications with respective different endurances by choosing a pair ofthe RRAM cell arrays (e.g., 204 and 206) to present respective originaland complementary logic states of information bits that are used inhigh-endurance applications and a single RRAM cell (e.g., e.g., 202) topresent original logic states of information bits that are used inlow-endurance applications. Moreover, the RRAM cells of such RRAM cellarrays that are used in different applications can be formed on a samechip (e.g., 102 of FIG. 1 ) by a single recipe.

FIG. 5D illustrates exemplary operation comparisons between two types ofsensing amplifier circuits, in accordance with some embodiments. Thefirst sensing amplifier (SA) circuit 585 utilizes one cell to representone bit (1c1b); while the second sensing amplifier (SA) circuit 595utilizes two cells to represent one bit (2c1b).

For the 1c1b circuit 585, a logic bit is determined by comparing thetarget cell current Icell_T with the reference current Iref. Two currentdistributions corresponding to two logic bits (0 and 1) respectively areshown in the operation plot 586 of the 1c1b circuit 585. A key parameterto an endurance of the 1c1b circuit 585 is the tail-to-tail window, i.e.the distance between the two tails, i.e. tail currents corresponding tologic 0 (IR0) and logic 1 (IR1), of the two distributions in theoperation plot 586. To distinguish between logic bits 0 and 1, thereference current Iref is put in the middle of the two tail currents ofIR0 and IR1. For example, to have an endurance margin of 5 uA, both thedistance between Iref and IR0 and the distance between Iref and IR1 needto be 5 uA. As such, a 10 uA tail-to-tail window is needed for the 1c1bcircuit 585 to achieve an endurance of 5 uA.

For the 2c1b circuit 595, a logic bit is determined by comparing thetarget cell current Icell_T with the complimentary current Icell_C thatalways represents a complimentary logic bit of that represented by theIcell_T. Two current distributions corresponding to two logic bits (0and 1) respectively are shown in the operation plot 596 of the 2c1bcircuit 595. A key parameter to an endurance of the 2c1b circuit 595 isalso the tail-to-tail window, i.e. the distance between the two tails ofthe two distributions of Icell_T and Icell_C. For example, to have anendurance margin of 5 uA, the distance between tails of Icell_T andIcell_C may be 5 uA (or even a smaller distance because it is veryunlikely for both Icell_T and Icell_C to fall into the worst case at thetwo tails at the same time). As such, only a 5 uA tail-to-tail window isneeded for the 2c1b circuit 595 to achieve an endurance of 5 uA.

That is, to achieve a same endurance, the 2c1b circuit 595 needs asmaller tail-to-tail window than the 1c1b circuit 585. Alternatively, byhaving a same tail-to-tail window, the 2c1b circuit 595 will have ahigher endurance than the 1c1b circuit 585. As discussed above, a samerecipe may be used to manufacture these two types of SA circuits in asame RRAM macro, to save cost and satisfy different enduranceapplications at the same time. The two types of SA circuits generated bythe same recipe will have same thickness and crystalline structure, butdifferent diameters and endurance levels.

FIG. 6 illustrates a flow chart of an exemplary method 600 to operatethe RRAM architecture 100, in accordance with various embodiments. Invarious embodiments, the operations of the method 600 are performed bythe respective components illustrated in FIGS. 1-5C. For purposes ofdiscussion, the following embodiment of the method 600 will be describedin conjunction with FIGS. 1-5C. The illustrated embodiment of the method600 is merely an example. Therefore, it should be understood that any ofa variety of operations may be omitted, re-sequenced, and/or added whileremaining within the scope of the present disclosure.

The method 600 starts with operation 602 in which an RRAM architectureincluding a plurality of RRAM cell arrays that share a universalvariable resistance dielectric layer is provided. In some embodiments,the plurality of RRAM cell arrays may share a same I/O circuit but eachof the RRAM cell arrays corresponds to a respective WL driver. In oneexample, such an RRAM architecture may include the RRAM architecture100. As discussed with reference to FIGS. 1 and 2 , the RRAMarchitecture 100 includes an RRAM macro 108 with at least three RRAMcell arrays 202, 204, and 206 disposed on the single chip 102, and theRRAM cells in each of the RRAM cell arrays include an universal variableresistance dielectric layer (e.g., 332 with references to FIG. 3 ) thatis formed by a single recipe.

The method 600 continues to operation 604 in which first and second RRAMcell arrays are selected to be used in a first application. Next, themethod 600 continues to operation 606 in which a third RRAM cell arrayis selected to be used in a second application. In some embodiments,such first and second applications require respective differentendurances, for example, the first application may require a higherendurance (e.g., data storage) and the second application may require alower endurance (e.g., eFuse). In some embodiments, such selection maybe performed by the control logic circuit 104. In some embodiments, thefirst and second, RRAM cell arrays are disposed at opposite sides of theshared I/O circuit 218.

The method 600 continues to operation 608 in which a first informationbit's original logic state and complementary logic state are written torespective RRAM cells of the first and second RRAM cell arrays. In someembodiments, the first information bit represents a portion of data usedin the first application that requires the higher endurance. In someembodiments, the RRAM cell of the first RRAM cell array is written intothe information bit's original logic state, and the RRAM cell of thesecond RRAM cell array is written into the information bit'scomplementary logic state.

Next, the method 600 continues to operation 610 in which a secondinformation bit's original logic state is written to an RRAM cell of thethird RRAM cell array. In some embodiments, the second information bitrepresents a portion of data used in the second application thatrequires the lower endurance. In some embodiments, the RRAM cell of thethird RRAM cell array is written into the information bit's originallogic state.

The method 600 continues to operation 612 in which the first informationbit's original logic state is determined based on current signalsconducting through the respective RRAM cells of the first and secondRRAM cell arrays. In some embodiments, since the first information bit'soriginal and complementary logic states are respectively written to theRRAM cells of the first and second RRAM cell arrays, the current signalsmay correspond to the first information bit's corresponding HRS (highresistance state) and LRS (low resistance state) current signals. Insome embodiments, the original and complementary logic states of thefirst information bit may be determined by the SA 458 of the shared I/Ocircuit 218. The method 600 continues to operation 614 in which thesecond information bit's original logic state is determined based on acurrent signal conducting through the RRAM cell of the third RRAM cellarray. In some embodiments, since the second information bit's originallogic state is written to the RRAM cell of the third RRAM cell array,the current signal may correspond to the second information bit'scorresponding HRS (high resistance state) or LRS (low resistance state)current signal (based on the second information's original logic state).In some embodiments, the original state of the second information bitmay be determined by the SA 458 of the shared I/O circuit 218.

FIG. 7 illustrates a flow chart of an exemplary method 700 to fabricatethe RRAM macro 108 of FIG. 2 , in accordance with some embodiments. Asdiscussed above, the RRAM macro 108 includes different RRAM cell arrays202, 204, 206. Each of the RRAM cell arrays 202, 204, 206 may include aresistor between a source line and a bit line. The resistor may beformed as a multi-layer stack that includes a top electrode, a cappingnode, a resistance dielectric, and a bottom electrode.

As shown in FIG. 7 , a source line layer is formed at operation 710. Atoperation 720, a bottom electrode layer including a plurality of bottomelectrodes is formed on the source line layer. Each of the plurality ofbottom electrodes is formed for a different RRAM cell. The bottomelectrodes are formed using a same single recipe but different layoutsizes for different cell arrays. As such, bottom electrodes in differentcell arrays 202, 204, 206 can have same thickness and crystallinestructure, but different diameters. At operation 730, a variableresistance dielectric layer including a plurality of resistancedielectrics is formed on the bottom electrode layer. Each of theplurality of resistance dielectrics is formed for a different RRAM cell.The resistance dielectrics are formed using a same single recipe butdifferent layout sizes for different cell arrays. As such, resistancedielectrics in different cell arrays 202, 204, 206 can have samethickness and crystalline structure, but different diameters. Atoperation 740, a capping layer including a plurality of capping nodes isformed on the variable resistance dielectric layer. Each of theplurality of capping nodes is formed for a different RRAM cell. Thecapping nodes are formed using a same single recipe but different layoutsizes for different cell arrays. As such, capping nodes in differentcell arrays 202, 204, 206 can have same thickness and crystallinestructure, but different diameters. At operation 750, a top electrodelayer including a plurality of top electrodes on the capping layer. Eachof the plurality of top electrodes is formed for a different RRAM cell.The top electrodes are formed using a same single recipe but differentlayout sizes for different cell arrays. As such, top electrodes indifferent cell arrays 202, 204, 206 can have same thickness andcrystalline structure, but different diameters. A bit line layer isformed on the top electrode layer at operation 760.

In an embodiment, a memory architecture includes: a plurality of cellarrays that each comprises a plurality of bit cells, wherein each of thebit cells of the plurality of cell arrays uses a respective variableresistance dielectric layer to transition between first and second logicstates; and a control logic circuit, coupled to the plurality of cellarrays, and configured to cause a first information bit to be writteninto respective bit cells of a pair of cell arrays as an original logicstate of the first information bit and a logically complementary logicstate of the first information bit, wherein the respective variableresistance dielectric layers are formed by using a same recipe ofdeposition equipment and have different diameters.

In another embodiment, a memory architecture includes: a first cellarray comprising a first plurality of bit cells; a second cell arraycomprising a second plurality of bit cells; a third cell arraycomprising a third plurality of bit cells; and a control logic circuit,coupled to the first, second, and third cell arrays, and configured tocause a first information bit to be written into respective bit cells ofthe first and second cell arrays as an original logic state of the firstinformation bit and a logically complementary logic state of the firstinformation bit, and a second information bit into a bit cell of thethird cell array as an original logic state of the second informationbit, such that the respective bit cells of the first and second cellarrays have a first endurance and the bit cell of the third cell arrayhas a second endurance, wherein the first endurance comprises a maximumnumber of cycles for which the respective bit cells of the first andsecond cell arrays can transition between respective differentresistance states, and the second endurance comprises a maximum numberof cycles for which the bit cell of the third cell array can transitionbetween respective different resistance states.

In yet another embodiment, a method includes: providing a memoryarchitecture comprising a plurality of memory cell arrays, whereinrespective memory cells of the plurality of memory cell arrays share auniversal variable resistance dielectric layer; selecting first andsecond memory cell arrays of the plurality of memory cell arrays to beused in a first application with a first endurance; selecting a thirdmemory cell array of the plurality of memory cell arrays to be used in asecond application with a second endurance; writing a first informationbit into respective memory cells of the first and second memory cellarrays as the first information bit's original and complementary logicstates; and writing a second information bit into a memory cell of thethird memory cell array as the second information bit's original logicstate, wherein the first endurance comprises a maximum number of cyclesfor which the respective memory cells of the first and second cellarrays can transition between respective different resistance states,and the second endurance comprises a maximum number of cycles for whichthe memory cell of the third cell array can transition betweenrespective different resistance states.

The foregoing outlines features of several embodiments so that thoseordinary skilled in the art may better understand the aspects of thepresent disclosure. Those skilled in the art should appreciate that theymay readily use the present disclosure as a basis for designing ormodifying other processes and structures for carrying out the samepurposes and/or achieving the same advantages of the embodimentsintroduced herein. Those skilled in the art should also realize thatsuch equivalent constructions do not depart from the spirit and scope ofthe present disclosure, and that they may make various changes,substitutions, and alterations herein without departing from the spiritand scope of the present disclosure.

What is claimed is:
 1. A memory device, comprising: a first cell arraycomprising a first plurality of bit cells using a first variableresistance dielectric layer to transition between logic states; a secondcell array comprising a second plurality of bit cells using a secondvariable resistance dielectric layer to transition between logic states;a third cell array comprising a third plurality of bit cells using athird variable resistance dielectric layer to transition between logicstates; and a control logic circuit configured to cause a firstinformation bit to be written into respective bit cells of the first andsecond cell arrays as an original logic state of the first informationbit and a logically complementary logic state of the first informationbit, and cause a second information bit to be written into a single bitcell of the third cell array as an original logic state of the secondinformation bit, wherein the first variable resistance dielectric layerhas a first diameter, and the third variable resistance dielectric layerhas a second diameter that is different from the first diameter.
 2. Thememory device of claim 1, wherein the first, second, and third variableresistance dielectric layers are formed based on a same recipe ofdeposition equipment, and share substantially an identical thicknessand/or crystalline structure.
 3. The memory device of claim 1, whereinthe first diameter is smaller than the second diameter.
 4. The memorydevice of claim 1, further comprising: a sensing circuit, coupled to thefirst, second and third pluralities of bit cells, and configured todetermine the first information bit's original logic state present bythe respective bit cells of the first and second cell arrays bycomparing respective current signals conducting through the respectivebit cells of the first and second cell arrays.
 5. The memory device ofclaim 4, wherein: the first and second cell arrays are disposed atrespective opposite sides of the sensing circuit; and the sensingcircuit is further configured to determine the second information bit'soriginal logic state present by the single bit cell of the third cellarray by comparing a current signal conducting through the single bitcell of the third cell array with a reference current signal.
 6. Thememory device of claim 1, wherein: each of the first, second and thirdpluralities of bit cells comprises a resistive random access memory(RRAM) bit cell; and the first, second and third cell arrays are formedas a memory macro disposed on a single chip.
 7. A memory device,comprising: a first cell array comprising a first plurality of bitcells; a second cell array comprising a second plurality of bit cells; athird cell array comprising a third plurality of bit cells; and acontrol logic circuit configured to cause a first information bit to bewritten into respective bit cells of the first and second cell arrays asan original logic state of the first information bit and a logicallycomplementary logic state of the first information bit, and a secondinformation bit into a bit cell of the third cell array as an originallogic state of the second information bit, such that the respective bitcells of the first and second cell arrays have a first endurance and thebit cell of the third cell array has a second endurance.
 8. The memorydevice of claim 7, wherein: the first endurance comprises a maximumnumber of cycles for which the respective bit cells of the first andsecond cell arrays can transition between respective differentresistance states; and the second endurance comprises a maximum numberof cycles for which the bit cell of the third cell array can transitionbetween respective different resistance states.
 9. The memory device ofclaim 7, wherein the first endurance is substantially higher than thesecond endurance.
 10. The memory device of claim 7, wherein: the first,second, and third pluralities of bit cells have a substantiallyidentical variable resistance dielectric layer; and the variableresistance dielectric layer comprises a thickness and crystallinestructure that is formed by using a same recipe of deposition equipment.11. The memory device of claim 7, further comprising: a sensing circuit,coupled to the first, second, and third cell arrays, and configured toread out the original logic state of the first information bit presentby the respective bit cells of the first and second cell arrays bycomparing respective current signals conducting through the respectivebit cells of the first and second cell arrays.
 12. The memory device ofclaim 11, wherein the first and second cell arrays are disposed atrespective opposite sides of the sensing circuit.
 13. The memory deviceof claim 11, wherein the sensing circuit is further configured to readout the original logic state of the second information bit present bythe bit cell of the third cell array by comparing a current signalconducting through the bit cell of the third cell array with a referencecurrent signal.
 14. The memory device of claim 7, wherein each of thefirst, second, and third pluralities of bit cells comprises a resistiverandom access memory (RRAM) bit cell.
 15. The memory device of claim 7,wherein: the first, second, and third cell arrays are formed as a memorymacro disposed on a single chip; and the first, second, and thirdpluralities of bit cells have respective variable resistance dielectriclayers that are formed by a same recipe of deposition equipment but havedifferent diameters.
 16. A memory device, comprising: a first cell arraycomprising a first plurality of bit cells using a first variableresistance dielectric layer to transition between logic states; a secondcell array comprising a second plurality of bit cells using a secondvariable resistance dielectric layer to transition between logic states;a third cell array comprising a third plurality of bit cells using athird variable resistance dielectric layer to transition between logicstates; and a control logic circuit configured to cause a firstinformation bit to be written into respective bit cells of the first andsecond cell arrays as an original logic state of the first informationbit and a logically complementary logic state of the first informationbit, and cause a second information bit to be written into a single bitcell of the third cell array as an original logic state of the secondinformation bit, wherein the first, second, and third variableresistance dielectric layers are formed based on a same recipe ofdeposition equipment, and have at least two different diameters.
 17. Thememory device of claim 16, wherein: each of the first and secondvariable resistance dielectric layers has a first diameter; the thirdvariable resistance dielectric layer has a second diameter; and thefirst diameter is smaller than the second diameter.
 18. The memorydevice of claim 16, further comprising: a sensing circuit, coupled tothe first, second and third pluralities of bit cells, and configured todetermine the first information bit's original logic state present bythe respective bit cells of the first and second cell arrays bycomparing respective current signals conducting through the respectivebit cells of the first and second cell arrays.
 19. The memory device ofclaim 18, wherein: the first and second cell arrays are disposed atrespective opposite sides of the sensing circuit; and the sensingcircuit is further configured to determine the second information bit'soriginal logic state present by the single bit cell of the third cellarray by comparing a current signal conducting through the single bitcell of the third cell array with a reference current signal.
 20. Thememory device of claim 16, wherein: each of the first, second and thirdpluralities of bit cells comprises a resistive random access memory(RRAM) bit cell; and the first, second and third cell arrays are formedas a memory macro disposed on a single chip.